1. Field of the Invention
The present invention relates to nonwoven fabric.
2. Related Art
Conventionally, nonwoven fabrics are used in a wide range of fields from hygienic products, such as baby diapers or feminine care articles (sanitary napkins) to cleaning products, such as wipers, or medical products, such as masks. Such nonwoven fabric is used in many different fields, but when actually used in products of each of those fields, it is necessary that the nonwoven fabric is manufactured with the properties and structures appropriate for their intended use.
Nonwoven fabric is manufactured by forming a fibrous layer (fiber web) using a dry method or a wet method, and then bonding the fibers that compose the fibrous layer together using a chemical bonding method or a thermal bonding method. There is a method of bonding the fibers, that compose the fibrous layer, in which a plurality of needles are repeatedly inserted into the fibrous layer, and there is a method wherein physical force, such as a blowing a race, is externally applied to the fibrous layer.
However, these methods only entangle the fibers and do not adjust the orientation or the arrangement of the fibers in the fibrous layer, or the shape of the fibrous layer. In other words, the fiber beds manufactured using these methods are simply sheet-shaped nonwoven fabric.
Also, if a predetermined liquid of excreta is applied to a nonwoven fiber used as a surface sheet of an absorbent material, for example, nonwoven fabric having an uneven surface are preferred to maintain or improve the feeling against the skin. For example, Japanese Patent No. 3587831 (hereinafter referred to as Patent Document 1) discloses nonwoven fabric formed with an uneven surface by heat contraction of a predetermined layer by laminating and thermally bonding a plurality of fibrous layers composed of fibers having different heat contraction characteristics, and a manufacturing method of the same.
These nonwoven fabrics are integrated when forming the uneven layer by laminating a plurality of fibrous layers and thermally bonding each fibrous layer. The result is high-density fibers, with low liquid-penetrability in many of the thermally-bonded areas. In addition, the areas can also sometimes be turned into a film. If the thermally bonded area turns into a film, it is even more difficult for the liquid to penetrate downward quickly.
Here, a second fibrous layer composed of non-heat-shrinkable fibers is laminated to a single side or both sides of a first fibrous layer including heat-shrunk heat-shrinkable fibers, the first fibrous layer and the second fibrous layer being integrated by a plurality of thermal bonding portions for the nonwoven fabric disclosed in Patent Document 1. In the thermal bonding portions, a plurality of convex portions is formed with the second fibrous layer projected by the heat shrinking of the first fibrous layer.
In other words, as shown by the nonwoven fabric and nonwoven fabric manufacturing method as described in Patent Document 1, conventionally, to form the fiber web into concave and convex portions, a plurality of fibrous layers having different properties is necessary. Therefore, the manufacturing processes are complicated. Also, if the first fibrous layer and the second fibrous layer are pulled apart during the heat shrinking process, the convex portions cannot be formed at the second fibrous layer, so it is necessary to securely bond the plurality of thermal-bonding portions of the first and the second fibrous layers. Therefore, fiber density at the thermally bonded portions is higher, and in some cases, the fibers are turned to film. This causes the problem of a thermally bonded area not being able to quickly pass a predetermined liquid of excreta, and the like. The present invention solves the aforementioned problems.